Papers by Author: Jing Sun

Abstract: To maintain the outlet temperature at the desired set-point, a high-order outlet temperature control model is established for a shell-and–tube heat exchanger, which is based on the analysis of its heat transfer process and dynamic properties .The Optimal PID control is applied to the temerature control system on the basis of this model, and the tuning parameters of the PID controller are obtained by numerical solving of a formulated optimization problem using Matlab/Simulink. An experimental control system is set up to testify the effect of the optimal PID control. The simulation result and the practice show that the control system has a favorable control performance.

Abstract: The composite materials TiN/3Y-TZP, 3Y-TZP doped by TiN with different contents and particle sizes, were fabricated through the same hot-pressing techniques. Compared with 3Y-TZP, the low temperature degradation resistance of TiN/3Y-TZP aged at the temperature from 170°C to 350°C in air for 50 h was investigated in virtue of XRD and SEM in the experiment. For TiN/3Y-TZP and 3Y-TZP, the maximum aging rate all occurs at 220°C. The addition of TiN can availably improve the low temperature degradation resistance of 3Y-TZP at different aging temperatures, but cannot change the relationship between the aging rate and the aging temperature. For TiN/3Y-TZP, the matrix particle size is the key factor responsible for its low temperature degradation resistance.

Abstract: The composite materials, 3Y-TZP added with TiN or/and Al2O3 particles, were fabricated by hot-pressing techniques. The effect of TiN and Al2O3 on the low temperature degradation of 3Y-TZP was investigated. It is shown that both TiN and Al2O3 can inhibit t-m transformation of 3Y-TZP and prevent the transformation from propagating into the specimen interiors when aged at a low temperature. The inhibition to the low temperature degradation of 3Y-TZP by Al2O3 is more sensitive to the aged temperature than by TiN. Compared with Al2O3, TiN is more available to inhibit t-m transformation on aged surfaces. The degradation resistance of 3Y-TZP codoped by TiN and Al2O3 is stronger than that of 3Y-TZP dispersed only by TiN or Al2O3.

Abstract: Ceramic tool materials, 3Y-TZP added by TiN particles, were fabricated through hot-pressing techniques. The effects of TiN on their low-temperature degradation at 220# in air were investigated. It is shown that TiN can improve the stability of t-ZrO2 and inhibit the transformation from tetragonal to monoclinic phase, and that the content of TiN affects the stability of tetragonal phase and the propagation of tetragonal-to-monoclinic transformation into the specimen interiors. It is suggested that the grain-boundary phase prevents the nucleation of transformation, and that the high elastic modulus of TiN can prevent the propagation of phase transformation by resisting the volume expansion of transformation. When the content of TiN is 20wt%, the ceramic material shows better low temperature degradation resistance.

Abstract: Ti(C0.7N0.3)-ZrO2-Ni-Mo cermet with 73.9%Ti(C0.7N0.3)-10%ZrO2-13%Ni-3.3%Mo(in mass) was fabricated by HP technology. The fabricated material possesses good mechanical properties with flexure strength (1264.4Mpa), fracture toughness (15 MPa.m1/2) and Vickers hardness (16.2GPa). The results of microstructure observation and analyses of the composite cermet by TEM, SEM and EDAX show that Mo2C nanoparticles are separated in the Ti(C,N) grains and the structure is similar to the “intragranular structure” in nanocomposite material. Smaller size t-ZrO2 and m-ZrO2 grains are distributed o n the boundaries of Ti(C,N) grains and the amount of m-ZrO2 is more than that of t-ZrO2.The growth of m-ZrO2 grain has an orientation on Ti(C,N) grain, which is propitious to the boundary bonding strength.

Abstract: In this paper, 3mol% yttria-stabilized tetragonal zirconia polycrystal (3Y-TZP) and TiN/3Y-TZP(adding TiN particles to 3Y-TZP) composites were fabricated by hot-pressing technique. Phase composition, microstructure and mechanical properties of the composites were investigated. It is shown that the flexural strength, fracture toughness and Vickers hardness of TiN/3Y-TZP was significantly improved by the addition of TiN particles compared with 3Y-TZP. The flexural strength of ZYT2 (20wt% TiN addition) is 1318 MPa. The fracture toughness of ZYT4 (40wt% TiN addition) is 16.8MPa·m1/2. The toughening and strengthening mechanisms were analyzed. The XRD results show that the additing of TiN can hinder the transformation from tetragonal phase to monoclinic phase of 3Y-TZP during fabrication process.

Abstract: Two kinds of Al2O3 /SiC nanocomposites with different alumina powder are developed, one is fabricated only by nano-scale alumina powders, the other is by micro-scale with partial nano-scale alumina powders. Both of the two composites may get higher flexural strength and fracture toughness than that of micro-scale monolithic alumina ceramics, but the latter is more preferable than the former. The microstructure and the strengthening and toughening mechanisms of the new ceramic tool materials are investigated, the improvement of mechanical properties may be mainly attributed to the transgranular fracture mode induced by the added nano-scale SiC, while adding nano-scale alumina powder to micro-scale powder, both of the nano-scale Al2O3 and nano-scale SiC may strengthen the micro-scale Al2O3 matrix, that means the nano-scale Al2O3 acted as the dispersed phase.